Automate inlined SVGs list in "Customize" docs

[ffoodd]

Could use regex in a dedicated shortcode, or maybe some kind of flag in our Sass files to locate SVGs?

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Could we make some shortcode to make it dynamic? Regexing SVG Data URi shouldn't be that hard. Ideally we'd get the corresponding file name to output, not sure is this is doable.

Originally posted by @ffoodd in #32759 (comment)

[mdo]

That'd be cool!